Nozzle for plasma welding torch

ABSTRACT

A nozzle assembly is provided which is adapted for use with a plasma torch and includes a threaded nozzle holder having cooling ducts therein and a threaded nozzle free of cooling ducts, and adapted to be screwed into the nozzle holder. The nozzle is fashioned with a conical contact surface which is adapted to rest against a corresponding contact surface in the nozzle holder and is designed, together with the threads of the nozzle and holder, so that a desired contact pressure between the conical surfaces of the nozzle and holder is maintained regardless of the temperature of the nozzle.

United States Patent 1 1 1111 3,851,824 Svensson Dec. 3, 1974 NOZZLE FOR PLASMA WELDING TORCH Primary ExaminerM. Henson Wood, Jr. [75] Inventor' g zgzf Svensson Taby Assistant ExarriinerMichael Y. Mar

Attorney, Agent,-0r Firm-Lerner, David, Littcnberg [73] Assignee: AGA Aktieholog, Lidingo, Sweden & Samuel [22] Filed: Mar. 21,1973 R C 57 ABST A T [21] Appl. No.: 343,222 1 A nozzle assembly 15 provlded wh1ch 1s adapted for use with a plasma torch and includes a threaded noz- U-S. Cl. le holder having cooling ducts therein and a threaded [51] Int. Cl B05b 15/00 nozzle f of cooling ducts, and adapted to be Fleld Of Search crewed into the nozzle 'holder The nozzle is fash- 239/600; I 6 ioned with a conical contact surface which is adapted to rest against a corresponding contact surface in the References Clted nozzle holder and is designed, together with the UNITED STATES PATENTS threads of the nozzle and holder, so that a desired 2,861,900 11/1958 Smith et al 239/1323 x Contact Pressure between the Conical surfaces of the 3,411,716 11/1968 Stephan et al. 239 1323 nozzle and holder is m int in regardless of the tem- FOREIGN PATENTS OR APPLICATIONS perature Of the nozzle 59,122 10/1921 Sweden 239/132 8 Clams 2 Drawing Figures FIELD OF INVENTION The present invention relates to a nozzle assembly for use in a plasma torch intended for plasma welding, plasma cutting, plasma surfacing or plasma spraying, which assembly comprises a threaded nozzle and a threaded nozzle holder which includes cooling ducts and is adapted to engage and retain said nozzle.

BACKGROUND OF THE INVENTION Conventional plasma torches include a nozzle fitted in a nozzle holder. Both the nozzle and nozzle holder include cooling ducts, connected to each other, and to a source of coolant such as water, so that direct cooling of the nozzle can be achieved. Furthermore, in order to avoid leakage, seals must be fitted between the nozzle and nozzle holder. The result is that a nozzle and holder of complicated design which include cooperating cooling ducts are required which are expensive to manufacture.

It is frequently necessary to replace worn-out nozzles in the afore-described plasma torches with new nozzles. However, the complexity of the required design of such nozzle and holder makes this task rather difficult.

BRIEF STATEMENT OF THE INVENTION In accordance with the present invention, there is provided anozzle assembly for a plasma torch, which is of uncomplicated design, does not require cooling ducts in the nozzle itself, and is adapted for easy nozzle replacement. Accordingly, the nozzle assembly of the invention overcomes the disadvantages associated with prior art nozzle assemblies.

The nozzle assembly of the present invention comprises a threaded nozzle holder, which is preferably internally threaded and includes a conical contact surface, means for cooling the assembly, disposed within said nozzle holder; and a threaded nozzle, which is preferably externally threaded, and includes a conical contact surface which is adapted to rest against said conical contact surface of said holder when said nozzle is threadably engaged in and pressed against said holder.

As will be seen hereinafter, the angle of slope of the conical contact surface of said nozzle or holder against the longitudinal axis of the plasma torch, and the diameter and the length of the threaded portions of said nozzle or holder are chosen so that the quotient of the radial and the axial movement of a surface element on said conical surface during heating up of said nozzle is always greater than the tangent of the angle of slope of said conical surface. Such a design will ensure that the desired contact pressure between the conical surfaces of said nozzle and bolder are maintained even when the temperature of the nozzle rises and the nozzle expands.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a cross-sectional view of a lower portion of i DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a preferred embodiment of the nozzle assembly of the invention is shown and is identified generally by the numeral 10. The assembly which comprises the lower portion of plasma torch 11, includes a nozzle holder 12. having internal threads 14 and conical contact surface 15, and provided with cooling ducts 16, which communicate with a source of coolant such as a water supply source, not shown for drawing clarity. A nozzle indicated generally by the numeral 20 includes external threads 22, nozzle opening 24, and conical contact surface 26.

The nozzle 20 is adapted to be threadably engaged or screwed into nozzle holder 12 so that the conical surface 26 thereof rests against conical surface 15 of the holder 12.

The heat generated in the nozzle 20 will be transferred via these contact surfaces 25, 15 to the holder 12, which, as mentioned previously, is water-cooled, whence the heat is carried off.

To avoid a reduction in contact pressure between the conical surfaces when the temperature of the nozzle rises and the nozzle expands, the angle of slope of the conical surface 26 or 15, and the diameter and length of the thread 22 are chosen so, that the quotient of the radial and the axial movement of a surface element on the conical surface is always greater than the tangent of the angle of slope [3 (shown in FIG. 2). In order to prevent the contact pressure at a point P of the conical surface with an angle of slope B from being reduced when the temperature of the nozzle increases by the amount A t the following condition may be drawn up. The diameter of the threaded part is put equal to D, the length of the thread equal to l, the distance from the start of the thread to the point A on the thread where axial movement in relation to the nozzle holder does not occur is equal to a" and the coeffecient of linear expansion is equal to a, as shown in FIG. 2. If it is assumed that the nozzle is uniformly heated and the temperature of the nozzle holder is not altered, the following applies for a surface element in the point P situated at a distance x from the start of the thread:

At a (D/2 xtgB) At a (x 0) 13B D/2 xtgfi'q (x gB If the angle of slope is selected to be equal to 45, we obtain In practice it is found that ,a" can never become greater than one-half. In the present case a becomes considerably less than one-half so that we obtain:

H2 or D l I sign, thereby, facilitating replacement of worn-out nozzles and is relatively inexpensive to manufacture primarily due .to the fact that cooling ducts are not required and are not present in the nozzle itself. Furthermore, owing to the design of the nozzle and holder, a

sufficient pressure is maintained at all times between the contact surfaces so that the heat is effectively carried off from the nozzle to the holder.

The nozzle assembly is not limited to the values which have been given above, but variations are certainly possible within the scope of the conditions specified in accordance with the invention. Furthermore, the nozzle assembly of the invention can be employed in conjunction with any conventional plasma torch as will be apparent to those skilled in the art.

What is claimed is:

1. A nozzle assembly for use with a plasma torch. comprising a threaded nozzle holder; a conical contact surface on said holder; means for cooling the assembly, disposed within said holder; a threaded nozzle and a conical contact surface thereon, adapted to rest against said conical contact surface on said holder, when said nozzle is threadably engaged in and thereby pressed against said holder, the angle of slope of the conical surface of said nozzle or holder against the longitudinal axis of the torch in which said assembly is disposed and the diameter (D) and length (l) of the threaded portion being chosen so, that the quotient of the radial and the axial movement of a surface element on said conical surface during heating up is always greater than the tangent of the angle of slope (B) of said conical surface.

2. The nozzle assembly in accordance with claim 1 wherein said holder includes internal threads and said nozzle includes external threads.

3. The nozzle assembly in accordance with claim 2 wherein said holder includes a centrally disposed bore, said internal threads being positioned in the interior walls defining said bore.

4. The nozzle assembly in accordance with claim 1 wherein said means for cooling the assembly comprise one or more cooling ducts disposed within said holder.

5. The nozzle assembly in accordance with claim 4 wherein said cooling ducts are in communication with a water supply.

6. The nozzle assembly in accordance with claim I when D 1 for the angle of slope (B) chosen.

7. The nozzle assembly in accordance with claim 1 wherein the distance from the start of the thread of said nozzle to a point (A) on the thread where axial movement in relation to the nozzle holder does not occur is equal to a and the coefficient of linear expansion is equal toa, then where the nozzle is uniformly heated so that the temperature thereof increases by the amount A r, and the temperature of the nozzle holder is not altered, the following applies for a surface element on the point P situated at a distance x from the start of the thread:

8. The nozzle assembly in accordance with claim 7 wherein a /2. 

1. A nozzle assembly for use with a plasma torch, comprising a threaded nozzle holder; a conical contact surface on said holder; means for cooling the assembly, disposed within said holder; a threadeD nozzle and a conical contact surface thereon, adapted to rest against said conical contact surface on said holder, when said nozzle is threadably engaged in and thereby pressed against said holder, the angle of slope of the conical surface of said nozzle or holder against the longitudinal axis of the torch in which said assembly is disposed and the diameter (D) and length (1) of the threaded portion being chosen so, that the quotient of the radial and the axial movement of a surface element on said conical surface during heating up is always greater than the tangent of the angle of slope ( Beta ) of said conical surface.
 2. The nozzle assembly in accordance with claim 1 wherein said holder includes internal threads and said nozzle includes external threads.
 3. The nozzle assembly in accordance with claim 2 wherein said holder includes a centrally disposed bore, said internal threads being positioned in the interior walls defining said bore.
 4. The nozzle assembly in accordance with claim 1 wherein said means for cooling the assembly comprise one or more cooling ducts disposed within said holder.
 5. The nozzle assembly in accordance with claim 4 wherein said cooling ducts are in communication with a water supply.
 6. The nozzle assembly in accordance with claim 1 when D > 1 for the angle of slope ( Beta ) chosen.
 7. The nozzle assembly in accordance with claim 1 wherein the distance from the start of the thread of said nozzle to a point (A) on the thread where axial movement in relation to the nozzle holder does not occur is equal to ''''a'''' and the coefficient of linear expansion is equal to Alpha , then where the nozzle is uniformly heated so that the temperature thereof increases by the amount Delta t, and the temperature of the nozzle holder is not altered, the following applies for a surface element on the point P situated at a distance x from the start of the thread: D/2 + xtg Beta > (x + a) tg Beta
 8. The nozzle assembly in accordance with claim 7 wherein ''''a'''' < 1/2 . 